uniform sampler2D texGround;
uniform sampler2D texRock;

varying float height;
varying vec2 Texcoord;

void main(void)
{
   vec4 a = texture2D( texGround, Texcoord );
   vec4 b = texture2D( texRock, Texcoord );
   gl_FragColor = mix(a,b,0.5);
}